Oracle acquired Sun Microsystems' Java technology when it bought the company earlier this year. Java is a software environment that allows applications written in Java to run on virtually any computer so long as it has a Java virtual machine installed.

When Google developed Android it included a Java compatible technology called Dalvik with the phone OS. Dalvik was developed as a "clean room" version of Java, meaning Google built it from the ground up without using any Sun technology or intellectual property, said Gartner analyst Ken Dulaney.

"You can't just take a Java application from a Sun environment, where it's licensed, and run it on Android. You have to recompile it to Dalvik," Dulaney said.

Oracle says Dalvik is a competitor to Java and infringes several of its patents, which it lists in the complaint, and its Java copyright.

It was unclear Thursday if Oracle approached Google to discuss its concerns before it filed the lawsuit.

Oracle's motivation was probably Android's recent success in the smartphone market, Dulaney said. "They own Sun now and they want to collect the royalties on the language," he said.

Oracle alleges that Google was aware of its patents and "willfully and deliberately" infringed them. It also says Google hired some of Sun's Java engineers. It wants the court to block the alleged infringement and award it damages.

Dulaney said Oracle's case could be "hard to prove" and that a legal battle could take a long time. "What they'll have to argue about is whether Google did a purely clean-room Java or if they have someone with inside knowledge of the code," he said.

Dalvik is one option for writing Android applications; developers can also use HTML 5 and the C language. But Dalvik is used for some of the core Android applications, such as email, Dulaney said.

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